1. Field of the Invention
The present invention generally relates to image decompression, and, in particular, to image decompression of decompressing image data in a form of wavelet transform coefficients or subband transform coefficients so as to obtain a decompressed image having a given size, in particular, a reduced-sized image such as a thumbnail image.
2. Description of the Related Art
A JPEG scheme which is a conventional encoding scheme for decompressing a coded natural image has been used for decompressing a coded image so as to obtain a decompressed image having a size same as that of an original image (see ISO/IEC 10918-1, ‘Information Technology Digital Compressing and Coding of Continuos-tone Still Images’). Therefore, in order to output a coded image to various output devices having different resolutions, expansion/reduction (change in the number of pixels) of an decompressed image should be previously performed. Moreover, in the related art, according to wavelet transform, a decompressed image has the same size as that of an original image. Accordingly, in order to obtain a decompressed image having a size according to a user's request, it is needed to perform a size-change process after performing wavelet inverse transform, so as to adjust the image size.